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Small‐angle Scattering Studies of Adsorption and of Capillary Condensation in Porous Solids
Author(s) -
Hoinkis Ernst
Publication year - 2004
Publication title -
particle and particle systems characterization
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.877
H-Index - 56
eISSN - 1521-4117
pISSN - 0934-0866
DOI - 10.1002/ppsc.200400927
Subject(s) - capillary condensation , adsorption , mesoporous material , saturation (graph theory) , condensation , capillary action , desorption , porous medium , materials science , porosity , vapor pressure , chemical engineering , percolation (cognitive psychology) , chemistry , analytical chemistry (journal) , thermodynamics , composite material , chromatography , organic chemistry , catalysis , physics , mathematics , combinatorics , neuroscience , biology , engineering
Small‐angle scattering (SAS) studies are reviewed of adsorption and capillary condensation of water, hydrocarbons and halogenated hydrocarbons near room temperature, and of nitrogen at 78 K in some mesoporous solids, mainly silicas. The theory needed for the interpretation of SAS data is briefly covered. Calculations of the scattered intensity I ( q ) for a model porous medium show that I ( q ) depends markedly on the film thickness t. Adsorption and capillary condensation of nitrogen at 78 K in mesoporous silicas was studied by use of in situ SANS, and t as function of the relative pressure P / P s was estimated. Adsorption of N 2 in defects within the silica skeleton at P / P s <0.1 lead to a significant increase in I ( q ). Isolated vapor bubbles in capillary condensed nitrogen in a Gelsil ® appeared on adsorption near saturation of the pore system. The kinetics of capillary condensation and of drainage were followed. Power law scattering at low q indicated the formation of ramified clusters of voids on drainage of liquid nitrogen from the xerogel Gelsil ® . Similar clusters were observed on drainage of water from Vycor ® glass. Provided the clusters indicate a percolation process, the desorption branch should not be used for the estimation of a pore size distribution for materials with networked pores. The adsorptive smoothing by benzene was observed of a rough interface in a controlled pore glass.